The invention relates to recovery of hydrocarbon gas from a wellbore, and more particularly, the invention relates to technology for separation of contaminants from hydrocarbon gas in a wellbore and selective recovery of hydrocarbon gas.
Hydrocarbon gases and liquids have been recovered from underground wellbores for over a hundred years. The recovery technology generally involves drilling a wellbore into a hydrocarbon gas or liquid formation and withdrawing the materials under reservoir pressure or by artificial lifting.
In hydrocarbon gas wells, the current recovery technology involves removing the hydrocarbon gas and any contaminants which are present from the wellbore together, and separating the contaminants from the hydrocarbon gas above ground. This above ground separation is costly. Disposal of the removed contaminants may also present environmental problems. The contaminants which may be produced include gases, such as carbon dioxide, nitrogen, water vapor, hydrogen sulfide, helium, and other trace gases, and liquids such as water, heavy hydrocarbons, and others.
The contaminants which are brought to the surface and separated from the hydrocarbon gas must be released to the atmosphere or otherwise disposed of adding additional expense to the process. Due to environmental concerns about the release of greenhouse gases, many countries are placing greater and greater limitations on emission of byproduct gases to the atmosphere. For example, some countries now access a tax on carbon dioxide emissions. Other gases are highly corrosive or poisonous and require special handling. For example, hydrogen sulfide must be reacted and converted to molten sulfur before disposal.
Accordingly, it would be highly desirable to maintain some or all of the contaminant materials within the wellbore and/or selectively separate these gases in the wellbore for reinjection, removal, or other processing.
Membrane technologies have been developed which allow the selective passage of materials. However, this technology has heretofore been used as a surface technology for separating hydrocarbons from contaminants after recovery and has not been used in a downhole situation. Accordingly, it would be desirable to provide an apparatus and method for downhole separation and selective recovery to maximize the production of a desired hydrocarbon gas while minimizing production or separately producing contaminants.
The present invention relates to a downhole preferential recovery technology for separation of contaminates such as carbon dioxide, nitrogen, water vapor, hydrogen sulfide, helium, trace gases, water, heavy hydrocarbons, and other contaminates from hydrocarbon gases.
In accordance with one aspect of the present invention, a method of separating gases in a wellbore includes the steps of: placing a wellbore within a production zone; removing a hydrocarbon gas from the wellbore; and removing at least one contaminant from the hydrocarbon gas with a system including a first preferentially selective material positioned in the wellbore and a second preferentially selective material positioned in the wellbore, wherein the first preferentially selective material is permeable to different materials than the second preferentially selective material.
In accordance with an additional aspect of the present invention, a system for separating gases in a wellbore includes a first preferentially selective material configured to be positioned in the wellbore and a second preferentially selective material configured to be positioned in the wellbore. The first preferentially selective material separates a first contaminant from a hydrocarbon gas and the second preferentially selective material separates a second contaminant from the hydrocarbon gas.
The present invention provides advantages of a safe and economical solution to the separation of gases within a wellbore.